Magnetic bubble domain chips are well known in the art and are used for non volatile storage of information represented by the magnetic bubble domains. In such chips, the storage area is typically surrounded by a guard rail which serves two purposes: (1) it prevents stray magnetic bubbles from entering the storage area of the chip and (2) it collects stray bubbles from inside the storage area when they come into contact with the guard rail, in order to ensure that these bubble domains are moved away from the storage area. In this manner, the guard rail prevents bubbles outside the storage area from moving to the storage devices themselves, and eliminates bubble domains which may stray from the storage devices and which might wander about the storage area.
In the prior art, guard rails are known which are comprised of discrete magnetic propagation elements forming propagation paths along which bubble domains move. An example of such a guard rail is one comprised of permalloy T and I bars or chevron elements, such as that shown in U. S. Pat. Nos. 3,810,132 and 3,868,661. Since the propagation elements are discrete from one another, stray bubble domains can contact the guard rail from either side of it and will be propagated in a single, desired direction. However, for contiguous propagation element devices, guard rails are not easily provided.
Since contiguous propagation element patterns move bubble domains in one direction on one side of the pattern and in the opposite direction on the other side of the pattern, for the same magnetic field reorientation sequence, it is easy to prevent stray bubble domains from entering the storage area. For example, an ion implanted strip encircling the storage area of the bubble chip would prevent bubble domains from passing into the storage area, since bubble domains cannot move easily through a non ion implanted region. However, such an encircling border would also prevent stray bubble domains from leaving the general storage area of the chip and therefore the second purpose of the guard rail would not be achieved.
While it is conceptually possible to use a guard rail comprised of discrete propagation elements (e.g., conventional T-bar or chevron elements) in combination with an active storage area comprising contiguous propagation elements, such a design is not advisable since additional processing steps would be required. That is, the entire bubble chip could not be fabricated in a single masking step, but would require an additional masking step and an additional alignment procedure.
Accordingly, it is a primary object of this invention to provide a magnetic bubble domain chip having a guard rail suitable for use with contiguous element bubble propagation devices.
It is another object of this invention to provide a bubble domain chip using contiguous propagation elements and having a guard rail thereon which can be fabricated in the same masking step as that used to make the other devices on the bubble chip.
It is still another object of the present invention to provide a guard rail for a bubble domain chip using contiguous element structures, where the guard rail structure can be used to provide current carrying functions in addition to preventing adverse effects due to stray magnetic bubble domains in the magnetic bubble chip.
It is another object of the present invention to provide a magnetic bubble domain chip having contiguous propagation element structures and a guard rail comprised of contiguous elements, where both sides of the guardrail tend to move bubble domains in the same direction for the same sense of reorientation of the magnetic drive field.